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Date:   Wed, 10 Apr 2019 14:12:28 +0100
From:   Stefan Hajnoczi <stefanha@redhat.com>
To:     Dongli Zhang <dongli.zhang@oracle.com>
Cc:     linux-scsi@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        linux-block@vger.kernel.org, mst@redhat.com, jasowang@redhat.com,
        axboe@kernel.dk, jejb@linux.ibm.com, martin.petersen@oracle.com,
        cohuck@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] scsi: virtio_scsi: limit number of hw queues by
 nr_cpu_ids
Message-ID: <20190410131228.GB8210@stefanha-x1.localdomain>
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On Wed, Mar 27, 2019 at 06:36:35PM +0800, Dongli Zhang wrote:
> When tag_set->nr_maps is 1, the block layer limits the number of hw queues
> by nr_cpu_ids. No matter how many hw queues are used by virtio-scsi, as it
> has (tag_set->nr_maps =3D=3D 1), it can use at most nr_cpu_ids hw queues.
>=20
> In addition, specifically for pci scenario, when the 'num_queues' specifi=
ed
> by qemu is more than maxcpus, virtio-scsi would not be able to allocate
> more than maxcpus vectors in order to have a vector for each queue. As a
> result, it falls back into MSI-X with one vector for config and one shared
> for queues.
>=20
> Considering above reasons, this patch limits the number of hw queues used
> by virtio-scsi by nr_cpu_ids.
>=20
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
>  drivers/scsi/virtio_scsi.c | 1 +
>  1 file changed, 1 insertion(+)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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